The current project is the beginning of a three-phase investigation of the external validity of childhood disruptive and depressive disorders. The aim of the project is to compare disruptive and disruptive/depressive children on four main classes of dependent variables: Background (socioeconomic status, parenting styles, living circumstances); Individual (cognitive, academic, and attentional performance at referral); Treatment Response (initial responsiveness to medication of behavioral management); and Outcome (psychiatric, cognitive, and behavioral status at 16 and again at 21 years of age). In this initial Diagnostic and Treatment Response phase of the project, 192 male out-patients between 7 and 11 years of age will be studied over a four-year period. Six diagnostic subgroups will be formed: Exclusively Hyperactive; Exclusively Aggressive; Comorbid Hyperactive and Aggressive; Comorbid Hyperactive and Depressive; Comorbid Aggressive and Depressive; and Mixed Hyperactive/Aggressive/Depressive. After a baseline diagnostic assessment, each child will be randomly assigned to receive either 10 weeks of a placebo-controlled pharmacological treatment (methylphenidate) or 10 weeks of a psychological treatment (behaviorally oriented parent group training). Planned multivariate analyses will address questions of divergent validity and comorbidity. Two diagnostic systems will be studied and then compared: Loney's Two-Dimensional model and the DSM (III, III-R, and IV) system. A central substantive question is whether subgroups within and across the two diagnostic models have different prevalence, background factors, or treatment response. A central methodological aim is to compare empirical and clinical methods for combining diagnostic data from scales, sources, and settings. A final goal of these activities is to derive sound proposals for unifying the diagnosis of disruptive children.